EFFECTS OF RNASE AND RNA ON INVITRO ASTER ASSEMBLY

RNase alters the in vitro assembly of spindle asters in homogenates of meiotically dividing surf clam (Spisula solidissima) oocytes. Some effects of RNase, such as reduced astral fiber length, appear nonenzymatic and probably result from RNase binding to tubulin. RNase-induced changes in the microtuble organizing center are observed. Since other polycations can mimic RNase effects, the existence of an RNA component of the spindle organizing center remains uncertain. RNase and other polycations effects on astral fiber length can be prevented and reversed by the RNase inhibitor, poly-G, which can augment astral fiber length in the absence of added RNase or other polycations. Augmentation by poly-G is favored by high ionic strength, and can be duplicated by poly-U and, with less efficiency, by poly-A. Poly-C and unfractionated yeast RNA, are unable to augment aster assembly. Poly-G acid can augment the length of astral fibers on complete spindles isolated under polymerizing conditions. Specific polyribonucleotides can alter spindle assembly in vitro. The presence of an inhibitor of microtubule assembly in Spisula oocytes, which can be inactivated by specific RNA, is suggested.